Due to the increasing popularity of easy-care fabrics made of synthetic fibers as well as the ever increasing energy costs and growing ecological concerns of detergent users, the once popular warm and hot water washes have now taken a back seat to washing fabrics in cold water (30° C. and below). Many commercially available laundry detergents are even advertised as being suitable for washing fabrics at 15° C. or even 9° C. To achieve satisfactory washing results at such low temperatures, results comparable to those obtained with hot water washes, the demands on low-temperature detergents are especially high.
Branched surfactants are known to be particularly effective under cold water washing conditions. For example, surfactants having branching towards the center of the carbon chain of the hydrophobe, known as mid-chain branched surfactants, are known for cold-water cleaning benefits. 2-alkyl branched or “beta branched” primary alkyl sulfates (also referred to as 2-alkyl primary alcohol sulfates) are also known. 2-alkyl branched primary alkyl sulfates have 100% branching at the C2 position (C1 is the carbon atom covalently attached to the sulfate moiety). 2-alkyl branched alkyl sulfates are generally derived from 2-alkyl branched alcohols (as hydrophobes). 2-alkyl branched alcohols, e.g., 2-alkyl-1-alkanols or 2-alkyl primary alcohols, which are derived from the oxo process, are commercially available from Sasol, as ISALCHEM®. 2-alkyl branched alcohols (and the 2-alkyl branched alkyl sulfates derived from them) are positional isomers, where the location of the hydroxymethyl group (consisting of a methylene bridge (—CH2— unit) connected to a hydroxy (—OH) group) on the carbon chain varies. Thus, a 2-alkyl branched alcohol is generally composed of a mixture of positional isomers. Also, commercially available 2-alkyl branched alcohols include some fraction of linear alcohols. For example, Sasol's ISALCHEM® alcohols are prepared from Sasol's oxo-alcohols (LIAL® Alcohols) by a fractionation process that yields greater than or equal to 90% 2-alkyl branched material, with the remainder being linear material. 2-alkyl branched alcohols are also available in various chain lengths. 2-alkyl primary alcohol sulfates having alkyl chain length distributions from twelve to twenty carbons are known. ISALCHEM® alcohols in the range of C9-C17 (single cuts and blends), including ISALCHEM® 145 (C14-C15-alcohols) and ISALCHEM® 167 (C16-C17-alcohols), are commercially available.
Laundry detergents containing a commercial C14/C15 branched primary alkyl sulfate, namely LIAL® 145 sulfate, which contains 61% branching and 30% C4 or greater branching (branch contains at least four carbon atoms), are known. Detergents containing a mixture of a straight chain primary alkyl sulfate and a beta-branched chain primary alcohol sulfate, where the total number of carbon atoms ranges from 12 to 20, e.g., a branched chain C16 primary alcohol sulfate having 67% 2-methyl and 33% 2-ethyl branching, are known.
There is a continuing need for a branched surfactant that can improve cleaning performance at low wash temperatures, e.g., at 30° C. or even lower, at a reasonable cost and without interfering with the production and the quality of the laundry detergents in any way. Surprisingly, it has been found that the detergent compositions of the invention, which contain 2-alkyl primary alcohol sulfates having specific alkyl chain length distributions and/or specific fractions of certain positional isomers, provide increased grease removal (particularly in cold water).